The Dragonlance setting may seem like a pretty vanilla fantasy setting today, but it hides a lot of ideas which were innovative at the time for AD&D. The setting suffers a bit too much from NPC theatre for me: I want the PCs to be the special heros. But I admire the setting nonetheless for some really innovative design.
The Wizards of High Sorcery are one prime example of innovation. Not only do the red, black, and white wizards make some sense of a rather abstract mechanic (alignment) but they also get tied into the world with the three moons (gods of magic) and mechanically they had access to different sets of spells. This is huge for me, because you could run a wizard-heavy campaign and have some mechanically distinct characters, even if they're all wizards. This wasn't possible in basic D&D, and becomes difficult again in 4th edition. As someone who still dreams of running a Wizards' Guild type of game, this is huge.
In the Rule of Law setting that my back-home group plays in, we did something similar with the 3.5 wizards and sorcerers. The wizard class became part of a world-spanning wizards' guild where magic was heavily regulated. Sorcerers were hunted and villified because the guild couldn't regulate or control them. Two relatively similar classes become quite distinct with the right story.
Along the same lines, rather than the generic paladin/cavalier of the time, Dragonlance has its own unique order of knights. Later on in the timeline, we even get a dark mirror order of lawful evil antipaladins. These setting-specific orders for the classes (and come on, we'd be fine if they were just mechanically cavaliers or paladins) really give us a foundation to work with for some of the rarer classes. This, I like.
Reimagined races are another good example of the innovation here. While slightly annoying, the halflings (kender) and gnomes (tinkers) of Dragonlance really do help make the setting unique, along with some of the cultural differences betweeen the subraces of elves and dwarves. Furthermore, they do a pretty good job of having some unique villanous races (draconians) and avoiding some of the standards of fantasy (orcs). Its not a kitchen-sink fantasy world where everything can be found, and the races have some solid history and story behind them.
The last notable innovation is the specialty priests. No longer must each god grant the same array of clerical spells, but by dividing the cleric's list into spheres of influence (cf. Domains in third edition), the priests of the gods in Dragonlance are each unique. This level of customization isn't seen again in the official D&D line after second edition.
When all is said and done, I still don't really want to play or run a Dragonlance game. But I admire the setting, and its definitely worth a look for how to adapt things in one's own games.